Icing is a common natural phenomenon on cold surface. In our daily life, icing on cold surface will lower the operating efficiency of refrigerating equipment and cause huge energy waste, for example: the icing of the cooling towers of power plants, the icing of automobile carburetors, the icing of heat exchangers of refrigerating plants and the icing of refrigerators. As a frost layer has certain thermal isolating effect, the frost or ice on the surface of refrigerating equipment will impair the heat transfer efficiency of the equipment and narrow or even block the airflow channel, thereby resulting in huge energy waste. Generally speaking, a frost layer 5 mm thick in a refrigerator will reduce the refrigerating efficiency by about 20% and accordingly will increase the energy consumption by 20%; more seriously, icing on cold surface may cause a serious safety accident, for example: a plane may crash due to icing on fuselage. There are two ways to solve the frosting or icing on cold surface: One way is to thaw frost through additional energy consumption. In other words, when the frost layer reaches certain thickness, the frost will be thawed or scraped off through electric heating, electric pulse, external mechanical actions etc. These methods play a certain role in removing frost, but they all additionally consume a large amount of energy. Nowadays, energy is increasingly short, so these methods undoubtedly have great limitation. The second method is to apply an anti-frost coating on the cold surface to prevent the formation of frost on the cold surface, thereby realizing the objective of preventing frosting and saving energy.
At present, anti-frost coating mainly has two mechanisms to inhibit the formation of frost: the first mechanism is to make cold surface hydrophobic, increase the contact angle of water on the cold surface and reduce the contact area between water drips and the cold surface, thereby lengthening the condensation time of water drips and playing an effect of frost inhibition; meanwhile, hydrophobic surface may also weaken the attachment of water drips to surface and reduce frost formation. On the whole, cold hydrophobic surface has certain effect on inhibiting frost formation and reducing the thickness of frost layer, but as temperature of the cold surface drops, once frost is formed on the cold surface, the hydrophobic surface will lose its anti-frost effect. The second mechanism is to make cold surface hydrophilic. Relying on its hygroscopicity, hydrophilic material can absorb the water drips condensed on cold surface in the early stage of frosting and meanwhile lower the freezing point of water, thereby inhibiting frost formation.
There are mainly the following types of hydrophilic anti-frost coatings: firstly, anti-icing/frosting agents, such as: the anti-icing/frosting agents disclosed in CN 1061987A, CN 1044947A, CN 1048053A and CN 1104674A. This type of anti-frost material mainly uses ethanol, glycerol and propylene glycol, such that it is volatile and not durable. Secondly, a hydrophilic polymer coated with propylene glycol (Refer to CN1632014A): The hydrophilic components in this type of material are also volatile, and it not suitable to be used at low temperature (<−15° C.) and high humidity (>50%) because its anti-frost effect is affected by the temperature of the cold surface and ambient humidity. Thirdly, mixture of a hydrophilic polymer and an inorganic salt (such as: NaCl and KCl) (Refer to CN 1916094A): Although this type of material may be used under the condition of low temperature and high ambient humidity, the compatibility between inorganic salts and polymer is poor; and the migration of inorganic salts in the material will result in heterogeneity of the material, thereby impairing its anti-frost effect. More importantly, hydrophilic anti-frost coating is vulnerable to contamination. Once the material surface is contaminated, the anti-frost function will disappear.